<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<link rel="stylesheet" href="style.css" type="text/css">
<meta content="text/html; charset=iso-8859-1" http-equiv="Content-Type">
<meta name="viewport" content="width=device-width, initial-scale=1">
<link rel="Start" href="index.html">
<link rel="previous" href="Int64.html">
<link rel="next" href="Lexer.html">
<link rel="Up" href="index.html">
<link title="Index of types" rel=Appendix href="index_types.html">
<link title="Index of exceptions" rel=Appendix href="index_exceptions.html">
<link title="Index of values" rel=Appendix href="index_values.html">
<link title="Index of modules" rel=Appendix href="index_modules.html">
<link title="Index of module types" rel=Appendix href="index_module_types.html">
<link title="Arg" rel="Chapter" href="Arg.html">
<link title="Arg_helper" rel="Chapter" href="Arg_helper.html">
<link title="Array" rel="Chapter" href="Array.html">
<link title="ArrayLabels" rel="Chapter" href="ArrayLabels.html">
<link title="Ast_helper" rel="Chapter" href="Ast_helper.html">
<link title="Ast_invariants" rel="Chapter" href="Ast_invariants.html">
<link title="Ast_iterator" rel="Chapter" href="Ast_iterator.html">
<link title="Ast_mapper" rel="Chapter" href="Ast_mapper.html">
<link title="Asttypes" rel="Chapter" href="Asttypes.html">
<link title="Attr_helper" rel="Chapter" href="Attr_helper.html">
<link title="Bigarray" rel="Chapter" href="Bigarray.html">
<link title="Buffer" rel="Chapter" href="Buffer.html">
<link title="Builtin_attributes" rel="Chapter" href="Builtin_attributes.html">
<link title="Bytes" rel="Chapter" href="Bytes.html">
<link title="BytesLabels" rel="Chapter" href="BytesLabels.html">
<link title="Callback" rel="Chapter" href="Callback.html">
<link title="CamlinternalFormat" rel="Chapter" href="CamlinternalFormat.html">
<link title="CamlinternalFormatBasics" rel="Chapter" href="CamlinternalFormatBasics.html">
<link title="CamlinternalLazy" rel="Chapter" href="CamlinternalLazy.html">
<link title="CamlinternalMod" rel="Chapter" href="CamlinternalMod.html">
<link title="CamlinternalOO" rel="Chapter" href="CamlinternalOO.html">
<link title="Ccomp" rel="Chapter" href="Ccomp.html">
<link title="Char" rel="Chapter" href="Char.html">
<link title="Clflags" rel="Chapter" href="Clflags.html">
<link title="Complex" rel="Chapter" href="Complex.html">
<link title="Condition" rel="Chapter" href="Condition.html">
<link title="Config" rel="Chapter" href="Config.html">
<link title="Consistbl" rel="Chapter" href="Consistbl.html">
<link title="Depend" rel="Chapter" href="Depend.html">
<link title="Digest" rel="Chapter" href="Digest.html">
<link title="Docstrings" rel="Chapter" href="Docstrings.html">
<link title="Dynlink" rel="Chapter" href="Dynlink.html">
<link title="Ephemeron" rel="Chapter" href="Ephemeron.html">
<link title="Event" rel="Chapter" href="Event.html">
<link title="Filename" rel="Chapter" href="Filename.html">
<link title="Format" rel="Chapter" href="Format.html">
<link title="Gc" rel="Chapter" href="Gc.html">
<link title="Genlex" rel="Chapter" href="Genlex.html">
<link title="Graphics" rel="Chapter" href="Graphics.html">
<link title="GraphicsX11" rel="Chapter" href="GraphicsX11.html">
<link title="Hashtbl" rel="Chapter" href="Hashtbl.html">
<link title="Identifiable" rel="Chapter" href="Identifiable.html">
<link title="Int32" rel="Chapter" href="Int32.html">
<link title="Int64" rel="Chapter" href="Int64.html">
<link title="Lazy" rel="Chapter" href="Lazy.html">
<link title="Lexer" rel="Chapter" href="Lexer.html">
<link title="Lexing" rel="Chapter" href="Lexing.html">
<link title="List" rel="Chapter" href="List.html">
<link title="ListLabels" rel="Chapter" href="ListLabels.html">
<link title="Location" rel="Chapter" href="Location.html">
<link title="Longident" rel="Chapter" href="Longident.html">
<link title="Map" rel="Chapter" href="Map.html">
<link title="Marshal" rel="Chapter" href="Marshal.html">
<link title="Misc" rel="Chapter" href="Misc.html">
<link title="MoreLabels" rel="Chapter" href="MoreLabels.html">
<link title="Mutex" rel="Chapter" href="Mutex.html">
<link title="Nativeint" rel="Chapter" href="Nativeint.html">
<link title="Numbers" rel="Chapter" href="Numbers.html">
<link title="Obj" rel="Chapter" href="Obj.html">
<link title="Oo" rel="Chapter" href="Oo.html">
<link title="Parse" rel="Chapter" href="Parse.html">
<link title="Parser" rel="Chapter" href="Parser.html">
<link title="Parsetree" rel="Chapter" href="Parsetree.html">
<link title="Parsing" rel="Chapter" href="Parsing.html">
<link title="Pervasives" rel="Chapter" href="Pervasives.html">
<link title="Pparse" rel="Chapter" href="Pparse.html">
<link title="Pprintast" rel="Chapter" href="Pprintast.html">
<link title="Printast" rel="Chapter" href="Printast.html">
<link title="Printexc" rel="Chapter" href="Printexc.html">
<link title="Printf" rel="Chapter" href="Printf.html">
<link title="Profile" rel="Chapter" href="Profile.html">
<link title="Queue" rel="Chapter" href="Queue.html">
<link title="Random" rel="Chapter" href="Random.html">
<link title="Scanf" rel="Chapter" href="Scanf.html">
<link title="Set" rel="Chapter" href="Set.html">
<link title="Simplif" rel="Chapter" href="Simplif.html">
<link title="Sort" rel="Chapter" href="Sort.html">
<link title="Spacetime" rel="Chapter" href="Spacetime.html">
<link title="Stack" rel="Chapter" href="Stack.html">
<link title="StdLabels" rel="Chapter" href="StdLabels.html">
<link title="Str" rel="Chapter" href="Str.html">
<link title="Stream" rel="Chapter" href="Stream.html">
<link title="String" rel="Chapter" href="String.html">
<link title="StringLabels" rel="Chapter" href="StringLabels.html">
<link title="Strongly_connected_components" rel="Chapter" href="Strongly_connected_components.html">
<link title="Syntaxerr" rel="Chapter" href="Syntaxerr.html">
<link title="Sys" rel="Chapter" href="Sys.html">
<link title="Targetint" rel="Chapter" href="Targetint.html">
<link title="Tbl" rel="Chapter" href="Tbl.html">
<link title="Terminfo" rel="Chapter" href="Terminfo.html">
<link title="Thread" rel="Chapter" href="Thread.html">
<link title="ThreadUnix" rel="Chapter" href="ThreadUnix.html">
<link title="Typemod" rel="Chapter" href="Typemod.html">
<link title="Uchar" rel="Chapter" href="Uchar.html">
<link title="Unix" rel="Chapter" href="Unix.html">
<link title="UnixLabels" rel="Chapter" href="UnixLabels.html">
<link title="Warnings" rel="Chapter" href="Warnings.html">
<link title="Weak" rel="Chapter" href="Weak.html"><title>Lazy</title>
</head>
<body>
<div class="navbar"><a class="pre" href="Int64.html" title="Int64">Previous</a>
&nbsp;<a class="up" href="index.html" title="Index">Up</a>
&nbsp;<a class="post" href="Lexer.html" title="Lexer">Next</a>
</div>
<h1>Module <a href="type_Lazy.html">Lazy</a></h1>

<pre><span id="MODULELazy"><span class="keyword">module</span> Lazy</span>: <code class="code"><span class="keyword">sig</span></code> <a href="Lazy.html">..</a> <code class="code"><span class="keyword">end</span></code></pre><div class="info module top">
<div class="info-desc">
<p>Deferred computations.</p>
</div>
</div>
<hr width="100%">

<pre><span id="TYPEt"><span class="keyword">type</span> <code class="type">'a</code> t</span> = <code class="type">'a lazy_t</code> </pre>
<div class="info ">
<div class="info-desc">
<p>A value of type <code class="code"><span class="keywordsign">'</span>a&nbsp;<span class="constructor">Lazy</span>.t</code> is a deferred computation, called
   a suspension, that has a result of type <code class="code"><span class="keywordsign">'</span>a</code>.  The special
   expression syntax <code class="code"><span class="keyword">lazy</span>&nbsp;(expr)</code> makes a suspension of the
   computation of <code class="code">expr</code>, without computing <code class="code">expr</code> itself yet.
   "Forcing" the suspension will then compute <code class="code">expr</code> and return its
   result.</p>

<p>Note: <code class="code">lazy_t</code> is the built-in type constructor used by the compiler
   for the <code class="code"><span class="keyword">lazy</span></code> keyword.  You should not use it directly.  Always use
   <code class="code"><span class="constructor">Lazy</span>.t</code> instead.</p>

<p>Note: <code class="code"><span class="constructor">Lazy</span>.force</code> is not thread-safe.  If you use this module in
   a multi-threaded program, you will need to add some locks.</p>

<p>Note: if the program is compiled with the <code class="code">-rectypes</code> option,
   ill-founded recursive definitions of the form <code class="code"><span class="keyword">let</span>&nbsp;<span class="keyword">rec</span>&nbsp;x&nbsp;=&nbsp;<span class="keyword">lazy</span>&nbsp;x</code>
   or <code class="code"><span class="keyword">let</span>&nbsp;<span class="keyword">rec</span>&nbsp;x&nbsp;=&nbsp;<span class="keyword">lazy</span>(<span class="keyword">lazy</span>(...(<span class="keyword">lazy</span>&nbsp;x)))</code> are accepted by the type-checker
   and lead, when forced, to ill-formed values that trigger infinite
   loops in the garbage collector and other parts of the run-time system.
   Without the <code class="code">-rectypes</code> option, such ill-founded recursive definitions
   are rejected by the type-checker.</p>
</div>
</div>


<pre><span id="EXCEPTIONUndefined"><span class="keyword">exception</span> Undefined</span></pre>

<pre><span id="VALforce"><span class="keyword">val</span> force</span> : <code class="type">'a <a href="Lazy.html#TYPEt">t</a> -> 'a</code></pre><div class="info ">
<div class="info-desc">
<p><code class="code">force&nbsp;x</code> forces the suspension <code class="code">x</code> and returns its result.
   If <code class="code">x</code> has already been forced, <code class="code"><span class="constructor">Lazy</span>.force&nbsp;x</code> returns the
   same value again without recomputing it.  If it raised an exception,
   the same exception is raised again.
   Raise <a href="Lazy.html#EXCEPTIONUndefined"><code class="code"><span class="constructor">Lazy</span>.<span class="constructor">Undefined</span></code></a> if the forcing of <code class="code">x</code> tries to force <code class="code">x</code> itself
   recursively.</p>
</div>
</div>

<pre><span id="VALforce_val"><span class="keyword">val</span> force_val</span> : <code class="type">'a <a href="Lazy.html#TYPEt">t</a> -> 'a</code></pre><div class="info ">
<div class="info-desc">
<p><code class="code">force_val&nbsp;x</code> forces the suspension <code class="code">x</code> and returns its
    result.  If <code class="code">x</code> has already been forced, <code class="code">force_val&nbsp;x</code>
    returns the same value again without recomputing it.
    Raise <a href="Lazy.html#EXCEPTIONUndefined"><code class="code"><span class="constructor">Lazy</span>.<span class="constructor">Undefined</span></code></a> if the forcing of <code class="code">x</code> tries to force <code class="code">x</code> itself
    recursively.
    If the computation of <code class="code">x</code> raises an exception, it is unspecified
    whether <code class="code">force_val&nbsp;x</code> raises the same exception or <a href="Lazy.html#EXCEPTIONUndefined"><code class="code"><span class="constructor">Lazy</span>.<span class="constructor">Undefined</span></code></a>.</p>
</div>
</div>

<pre><span id="VALfrom_fun"><span class="keyword">val</span> from_fun</span> : <code class="type">(unit -> 'a) -> 'a <a href="Lazy.html#TYPEt">t</a></code></pre><div class="info ">
<div class="info-desc">
<p><code class="code">from_fun&nbsp;f</code> is the same as <code class="code"><span class="keyword">lazy</span>&nbsp;(f&nbsp;())</code> but slightly more efficient.</p>

<p><code class="code">from_fun</code> should only be used if the function <code class="code">f</code> is already defined.
    In particular it is always less efficient to write
    <code class="code">from_fun&nbsp;(<span class="keyword">fun</span>&nbsp;()&nbsp;<span class="keywordsign">-&gt;</span>&nbsp;expr)</code> than <code class="code"><span class="keyword">lazy</span>&nbsp;expr</code>.</p>
</div>
<ul class="info-attributes">
<li><b>Since</b> 4.00.0</li>
</ul>
</div>

<pre><span id="VALfrom_val"><span class="keyword">val</span> from_val</span> : <code class="type">'a -> 'a <a href="Lazy.html#TYPEt">t</a></code></pre><div class="info ">
<div class="info-desc">
<p><code class="code">from_val&nbsp;v</code> returns an already-forced suspension of <code class="code">v</code>.
    This is for special purposes only and should not be confused with
    <code class="code"><span class="keyword">lazy</span>&nbsp;(v)</code>.</p>
</div>
<ul class="info-attributes">
<li><b>Since</b> 4.00.0</li>
</ul>
</div>

<pre><span id="VALis_val"><span class="keyword">val</span> is_val</span> : <code class="type">'a <a href="Lazy.html#TYPEt">t</a> -> bool</code></pre><div class="info ">
<div class="info-desc">
<p><code class="code">is_val&nbsp;x</code> returns <code class="code"><span class="keyword">true</span></code> if <code class="code">x</code> has already been forced and
    did not raise an exception.</p>
</div>
<ul class="info-attributes">
<li><b>Since</b> 4.00.0</li>
</ul>
</div>

<pre><span id="VALlazy_from_fun"><span class="keyword">val</span> lazy_from_fun</span> : <code class="type">(unit -> 'a) -> 'a <a href="Lazy.html#TYPEt">t</a></code></pre><div class="info ">
<div class="info-deprecated">
<span class="warning">Deprecated.</span>synonym for <code class="code">from_fun</code>.</div>
</div>

<pre><span id="VALlazy_from_val"><span class="keyword">val</span> lazy_from_val</span> : <code class="type">'a -> 'a <a href="Lazy.html#TYPEt">t</a></code></pre><div class="info ">
<div class="info-deprecated">
<span class="warning">Deprecated.</span>synonym for <code class="code">from_val</code>.</div>
</div>

<pre><span id="VALlazy_is_val"><span class="keyword">val</span> lazy_is_val</span> : <code class="type">'a <a href="Lazy.html#TYPEt">t</a> -> bool</code></pre><div class="info ">
<div class="info-deprecated">
<span class="warning">Deprecated.</span>synonym for <code class="code">is_val</code>.</div>
</div>
</body></html>